+ mm-hugetlb-allow-overcommitting-gigantic-hugepages.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/hugetlb: allow overcommitting gigantic hugepages
has been added to the -mm mm-new branch.  Its filename is
     mm-hugetlb-allow-overcommitting-gigantic-hugepages.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb-allow-overcommitting-gigantic-hugepages.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

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------------------------------------------------------
From: Usama Arif <usamaarif642@gmail.com>
Subject: mm/hugetlb: allow overcommitting gigantic hugepages
Date: Mon, 6 Oct 2025 19:56:07 +0100

Currently, gigantic hugepages cannot use the overcommit mechanism
(nr_overcommit_hugepages), forcing users to permanently reserve memory via
nr_hugepages even when pages might not be actively used.

Remove this blanket restriction on gigantic hugepage overcommit.  This
will bring the same benefits to gigantic pages as hugepages:

- Memory is only taken out of regular use when actually needed
- Unused surplus pages can be returned to the system
- Better memory utilization, especially with CMA backing which can
  significantly increase the changes of hugepage allocation

Without this patch:
echo 3 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_overcommit_hugepages
bash: echo: write error: Invalid argument

With this patch:
echo 3 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_overcommit_hugepages
./mmap_hugetlb_test
Successfully allocated huge pages at address: 0x7f9d40000000

cat mmap_hugetlb_test.c
...
    unsigned long ALLOC_SIZE = 3 * (unsigned long) HUGE_PAGE_SIZE;
    addr = mmap(NULL,
                ALLOC_SIZE, // 3GB
                PROT_READ | PROT_WRITE,
                MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB | MAP_HUGE_1GB,
                -1,
                0);

    if (addr == MAP_FAILED) {
        fprintf(stderr, "mmap failed: %s\n", strerror(errno));
        return 1;
    }
    printf("Successfully allocated huge pages at address: %p\n", addr);
...

Link: https://lkml.kernel.org/r/20251006185607.3257340-1-usamaarif642@gmail.com
Signed-off-by: Usama Arif <usamaarif642@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Rik van Riel <riel@surriel.com>
Cc: Usama Arif <usamaarif642@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/hugetlb.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/mm/hugetlb.c~mm-hugetlb-allow-overcommitting-gigantic-hugepages
+++ a/mm/hugetlb.c
@@ -2232,7 +2232,7 @@ static struct folio *alloc_surplus_huget
 {
 	struct folio *folio = NULL;
 
-	if (hstate_is_gigantic(h))
+	if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
 		return NULL;
 
 	spin_lock_irq(&hugetlb_lock);
@@ -4294,7 +4294,7 @@ static ssize_t nr_overcommit_hugepages_s
 	unsigned long input;
 	struct hstate *h = kobj_to_hstate(kobj, NULL);
 
-	if (hstate_is_gigantic(h))
+	if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
 		return -EINVAL;
 
 	err = kstrtoul(buf, 10, &input);
@@ -5181,7 +5181,7 @@ static int hugetlb_overcommit_handler(co
 
 	tmp = h->nr_overcommit_huge_pages;
 
-	if (write && hstate_is_gigantic(h))
+	if (write && hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
 		return -EINVAL;
 
 	ret = proc_hugetlb_doulongvec_minmax(table, write, buffer, length, ppos,
_

Patches currently in -mm which might be from usamaarif642@gmail.com are

mm-hugetlb-allow-overcommitting-gigantic-hugepages.patch